Sentinel lymph node tumour burden using digital cell count estimation predicts outcomes in melanoma

Background and aims: Cutaneous melanoma often metastasises in primis to sentinel lymph nodes (SLNs). Currently, there is no standardized method of characterizing the micrometastatic tumour burden in SLN biopsies for melanoma. Different criteria have been developed to evaluate SLN biopsies, yet none consider the number of cells identified. Here, we used software analysis to digitally quantify metastatic tumour burden within SLNs and correlated these data with clinicopathological and prognostic information. Methods and results: We identified 246 cases of SLN biopsies, including 63 positive (26%) and183 (74%) negative for metastatic melanoma. Digital cell counting was performed within the greatest metastatic focus and the entire metastatic tumour burden within the same SLN. Increasing cell count in the largest metastatic deposit correlated with the previously described Rotterdam [Spearman's r = 0.91; 95% confidence interval (CI) = 0.84, 0.94], Starz (Spearman's r = 0.78; 95% CI = 0.68, 0.87) and Dewar criteria (P < 0.01), validating our method of using cell count to define SLN tumour burden. Additionally, increasing cell count was associated with decreased metastasis-free survival (hazard ratio = 2.29; 95% CI = 1.22, 4.31). Conclusion: These data support the use of computerized cell count analysis for prognostication of outcomes in patients undergoing SLN biopsy.